<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title></title>
  <style>
    canvas {
      box-shadow: 3px 3px 12px rgba(0, 0, 0, 0.5);
    }
  </style>
</head>
<body>
  <canvas id="canvas" width="640" height="480"></canvas>
  <script>
    const canvas = document.getElementById('canvas');
    const ctx = canvas.getContext('2d');
    
    const W = canvas.width;
    const H = canvas.height;
    
    // const gradient = ctx.createRadialGradient(W/2, H, 20, W/2, 0, 200);
    const gradient = ctx.createRadialGradient(W/2, H/2, 20, W/2, H/2, 400);
    
    gradient.addColorStop(0, 'rgb(230, 36, 36)');
    gradient.addColorStop(0.25, 'rgb(226, 242, 45)');
    gradient.addColorStop(0.5, 'rgb(33, 151, 236)');
    gradient.addColorStop(0.75, 'rgb(73, 224, 79)');
    gradient.addColorStop(1, 'rgb(52, 254, 211)');
    
    ctx.fillStyle = gradient;
    
    ctx.fillRect(0, 0, W, H);
  </script>
</body>
</html>